1. Field of the Invention
The present invention relates to a method of producing a high molecular weight organopolysiloxane by conducting the hydrolysis and condensation reaction of a silane compound containing a hydrolyzable group such as an organoalkoxysilane as a two-stage hydrolysis and condensation reaction, and also relates to a composition comprising a high molecular weight organopolysiloxane produced using such a method, and an optical semiconductor device comprising an optical semiconductor element sealed with a cured product of such a composition.
2. Description of the Prior Art
Methods of producing organopolysiloxanes by hydrolysis and condensation of organoalkoxysilanes are widely used in the silicone manufacturing industry. The most commonly used method for conducting hydrolysis of an organoalkoxysilane involves conducting a hydrolysis and condensation reaction using an acid catalyst such as acetic acid, hydrochloric acid, or sulfuric acid.
However, in systems that contain a large quantity of an organoalkoxysilane containing 3 or more hydrolyzable groups such as methyltrimethoxysilane, which readily undergoes condensation and gelling, if hydrolysis is conducted using an acid catalyst such as acetic acid, hydrochloric acid, or sulfuric acid, then the resulting high molecular weight organopolysiloxane polymer is unstable and is prone to immediate gelling.
Furthermore, coatings obtained by curing compositions comprising conventional organopolysiloxanes produced by hydrolysis-condensation of organotrialkoxysilanes have a high degree of hardness, and are consequently used for protecting plastic surfaces such as the plastic lenses used within spectacles and sunroofs within vehicles. However, these coatings typically have a thickness of 2 to 3 μm, and if the thickness is 10 μm or greater, then cracking becomes a problem. Furthermore, because these coatings exhibit excellent mechanical properties, heat resistance, and electrical insulating properties, they are also used as protective films and materials for interlayer insulation layers for electrical components and semiconductors, and also as photosensitive materials, pellicle materials and coating materials, but they are not used as hard thick films.
However, a coating produced by curing a composition comprising an organopolysiloxane produced by hydrolysis and condensation of a silane compound containing an organotrialkoxysilane as the primary component is hard, exhibits a high degree of thermal stability, and is a potential substitute material for glass, and consequently the development of a method of producing a high molecular weight organopolysiloxane capable of resolving the above problems has been keenly sought.